What Is the Primary Reason for Performing Left Uterine Displacement (LUD) During CPR on a Pregnant Patient: Why It Relieves Aortocaval Compression From About 20 Weeks

The primary reason is mechanical: from roughly 20 weeks of pregnancy, the gravid uterus compresses the inferior vena cava and aorta when the patient lies flat, and displacing the uterus to the patient's left lifts that weight off the great vessels so chest compressions can generate forward blood flow. Left uterine displacement, or LUD, is a maneuver, not a treatment — it buys hemodynamics while CPR and, ultimately, delivery do the actual work. It applies to a patient with a uterus large enough to cause aortocaval compression, which clinicians generally date from about 20 weeks' gestation or a fundal height at or above the umbilicus.

The Mechanical Answer: The Uterus Is Sitting on the Vena Cava and Aorta

Think of the pregnant abdomen as a weighted blanket draped over the body's two largest plumbing lines. The inferior vena cava runs just to the right of the spine, and the aorta sits just to its left. A uterus large enough to reach the umbilicus rests directly on both. That is the whole physical story behind LUD.

Venous return is the more dramatic casualty. The vena cava is a low-pressure, thin-walled vessel, so even modest external pressure collapses it. When it collapses, blood returning from the legs and lower body cannot reach the right heart, and cardiac output falls even before anything goes wrong with the heart itself. Chest compressions depend on that returning blood to fill the chest.

Arterial compression compounds matters. The aorta can be pressed against the spine, raising resistance to the blood the heart is trying to eject. Animal work on aortocaval compression during CPR has long suggested that relieving venous obstruction improves the hemodynamics compressions produce, while arterial obstruction is the harder problem to fully solve externally.

LUD attacks both lines at once by moving the uterus off the midline. The result is better preload for compressions and less outflow resistance. The purpose is not to fix the arrest — it is to remove a mechanical obstruction that makes every compression less effective than it should be.

Why About 20 Weeks and Umbilical Fundal Height Is the Trigger

The 20-week threshold is a practical line, drawn from when the uterus reliably becomes large enough to press on the vena cava. Before that point, aortocaval compression is much less likely to matter, and LUD adds little while complicating airway and chest access.

Fundal height is the bedside proxy. Roughly speaking, fundal height in centimeters tracks weeks of gestation between about 20 and 36 weeks. When the top of the uterus reaches the level of the umbilicus, typically around 20 to 22 weeks, the uterus has the bulk to compress the great vessels.

The American Heart Association's guidance for maternal cardiac arrest does not hinge on whether the fetus is viable. LUD is recommended once the uterus is at or above the umbilicus, because the maneuver protects the mother's circulation. Viability, a separate question, governs whether emergency delivery should follow — not whether the uterus needs to be moved.

Gestational age is often unknown in an arrest. A paramedic, a bedside nurse, or a first responder may have to guess from abdominal appearance or fundal height. When in doubt, displace.

What LUD Is Not: Versions, Supine Tilt, and the Manual Lift

LUD is often confused with tilting the whole patient, which is a different intervention with a different risk profile. Tilting the torso leftward does shift the uterus, but it also compromises the quality of chest compressions.

Modern guidance favors keeping the patient flat and displacing the uterus instead of tilting the board. Historically, the recommended range ran from 15 to 30 degrees of left lateral tilt; contemporary AHA maternal cardiac arrest guidance moved away from routine tilt in favor of manual LUD with the patient supine, largely because compressions stay more effective on a flat surface.

The maneuver itself takes a few recognizable forms. One is a one-handed push from the patient's right side, sliding the uterus toward the patient's left. Another is a two-handed pull from the patient's left, since the rescuer standing there can often get a better grip and tug the uterus leftward and slightly toward the head.

A third is a mechanical wedge or commercial device that pushes the uterus left while freeing the rescuer's hands. Each accomplishes the same displacement; the choice usually comes down to who is where and how much abdominal skin is exposed. Force should be gentle and steady, not a shove. The target is moving the uterus off the midline, not cracking ribs or harming the fetus.

How to Perform Left Uterine Displacement Without Stopping Compressions

LUD must fit into a resuscitation that is already crowded. The point is to keep compressions deep, fast, and uninterrupted while the uterus is moved, so rescuers need a division of labor before the arrest rather than a debate during it.

1: Confirm the need: uterus at or above the umbilicus, or gestation roughly 20 weeks or more by history or appearance. 2: Keep the patient supine on a firm surface, and assign a dedicated rescuer to the abdomen rather than the chest. 3: Place one hand on the right side of the abdomen near the uterine fundus and push the uterus steadily toward the patient's left until it sits clearly off the midline. 4: Alternatively, a rescuer on the patient's left grips the fundus and pulls it leftward and slightly cephalad, holding displacement continuously. 5: Maintain the displacement through the entire compression cycle; release only if it clearly prevents compressions, airway management, or defibrillation pad placement. 6: Reassess placement if compressions look less effective, and hand off the role when the compressor rotates, keeping displacement uninterrupted across the switch.

Failure handling falls into predictable patterns. If the patient's abdominal anatomy is obscured by obesity or distension, LUD may be hard to verify, and the rescuer should still displace and hold while focusing on compression quality. If displacement pulls at intravenous lines or surgical sites, use a two-handed, broader contact area rather than fingers. If the airway is being managed and a rescuer's hands are crowding the chest, the LUD hand stays lower on the abdomen near the fundus. If a device is available but unfamiliar, a trained human hand is usually faster on the first arrest.

Manual Hand Versus Wedge: Which LUD Method Fits Which Rescuer

Different teams reach for different tools, and the comparison below is about fit rather than superiority. All three approaches move the uterus off the great vessels; they differ in hands, setup time, and how much compression quality they protect.

The practical verdict depends on your team. If you have a designated "uterine displacer" role in your maternal arrest plan, the one-hand push is the simplest default and requires no equipment. If your kit already includes a wedge and your team trains with it, it frees a rescuer for airway or IV work at the cost of a small delay on the first use. Think of the choice as a staffing question more than a clinical one; no method should interrupt compressions for more than seconds.

LUD and the Rest of Maternal Cardiac Arrest: What It Does Not Replace

Displacement is one piece of a larger response, and its value depends on the rest being done well. It does not replace high-quality chest compressions at 100 to 120 per minute with full recoil, and it does not replace early defibrillation for a shockable rhythm.

It also does not replace preparation for perimortem cesarean delivery. AHA guidance ties the timing of emergency delivery to when the uterus is large enough to cause aortocaval compression, and the delivery itself resolves that compression definitively. LUD is the bridge; delivery, when indicated, is the structural fix.

Advanced life support proceeds alongside LUD. Airway management is harder in a late-stage pregnant patient because of reduced functional residual capacity and rapid oxygen desaturation, so airway steps compete for the space the LUD hand occupies. Drugs follow standard arrest dosing, with a recognized concern that pregnancy and a compressed vena cava can slow drug movement from a lower-extremity IV site; upper-extremity access is generally preferred.

The team leader's job is to sequence these elements rather than let any one crowd out the rest. If compressions are good and the uterus is displaced, the arrest care is on track. If the uterus is at the umbilicus and compressions have stopped for airway coaching, the larger problem is the pause.

Placental Perfusion: The Real Beneficiary Is the Mother

There is a common misconception that LUD is mainly for the fetus. In a maternal arrest, the fetus is a secondary concern until the mother's circulation is restored, and the physiology makes that concrete.

With the vena cava compressed, blood returning to the right heart falls, and forward flow from compressions falls with it. Cardiac output during CPR on a pregnant patient without relief of compression is generally lower than in a non-pregnant patient, which is part of why arrest survival in pregnancy is so dependent on getting the obstruction off the midline quickly.

Relieving the compression improves the preload available to compressions, and better compressions mean more blood reaching the placenta as well as the maternal brain. The fetus does benefit from good maternal hemodynamics, but it is a byproduct of treating the mother, not the target of the maneuver.

A useful framing for rescuers: the uterus is compressing the mother's return line, so moving it is a circulation intervention. Fetal outcome follows from maternal circulation. The priority order is not a value judgment about the pregnancy; it is physiology.

Two- Vs One-Rescuer Situations: Practical Squeezes on LUD Delivery

Real arrests happen in cramped places: a bathroom floor, a small bathroom-sized patient room, the back of an ambulance. Under those conditions, LUD competes for space with compressions, airway, and defibrillation.

In a two-rescuer team, one does compressions and one does LUD, and the airway waits or is managed by the same rescuer between cycles. This is a tight configuration that usually means LUD gets paused whenever the compressor rotates, so the hand-off should include moving the displacing hand.

In a larger team, a designated abdominal rescuer can hold LUD continuously while the compressor rotates around them. The practical reason to name the role in advance is that no one improvises a good two-handed grip on a slippery abdomen while talking through a megacode.

Space changes the ballet. If the patient is against a wall on the right side, a rescuer cannot reach from the right, so the pull-from-the-left technique becomes the only option. If the patient is in a narrow hallway, a wedge may not fit. The rule that survives all of it: keep compressions going and move the uterus off midline however your team can.

Training, Drills, and the Measurement That Matters Most

Displacement is a psychomotor skill, and skills that are not rehearsed do not appear under stress. Most teams that respond to maternal arrest practice a dedicated drill where one rescuer is assigned to the abdomen, because the natural instinct is for everyone to crowd the chest.

The quality markers worth tracking in a drill are simple. Time from recognition to first displacement, whether displacement continued across compressor rotations, and whether any pause in compressions occurred for the sake of the maneuver. A team that gets displacement started within 10 seconds of recognizing a late-pregnancy arrest is doing well.

Maternal cardiac arrest is rare enough that many clinicians will go years without seeing one. Simulation-based maternal arrest training is the accepted way to build and retain the skill, and it typically bundles compressions, airway, LUD, defibrillation, and the decision about delivery into one scenario.

Measurement should focus on the maneuver's continuity, not just its occurrence. A single correct push that is dropped at the first compressor switch is functionally a different intervention from displacement held through the whole cycle. The metric that matters is whether the uterus stayed off the midline whenever compressions were happening.

Scope, Limits, and When to Call for Help

This article covers the physiology and technique of left uterine displacement as general educational information. It is not a treatment plan or a substitute for the clinical protocols your service uses, and it does not replace hands-on training.

Local protocols vary by region and by provider type. Emergency medical services, obstetric units, and emergency departments may each have their own maternal arrest algorithm, and inpatient versus prehospital teams often have different equipment and staffing. Check the version your service uses. In the United States, AHA guidance and institutional protocols govern details; elsewhere, national resuscitation councils issue equivalents. A doctor or nurse on scene is the clinical authority, not this article.

Late pregnancy is also a time to be alert to the non-cardiac causes of arrest — hemorrhage, eclampsia, sepsis, pulmonary embolism — which are addressed by the treating team alongside the maneuvers described here. LUD is one maneuver in a resuscitation built around the specific cause. That context belongs to your clinical team, not to a general explainer.

FAQ

Does left uterine displacement help if the patient is only 16 weeks pregnant?

Generally no, because a 16-week uterus is below the umbilicus and unlikely to compress the vena cava enough to matter. The useful rule is fundal height at or above the umbilicus, which corresponds to roughly 20 weeks. At 16 weeks, treat the arrest per standard adult protocol and reassess the abdomen as the resuscitation proceeds.

Should the patient be tilted left instead of displaced manually?

Modern maternal cardiac arrest guidance favors keeping the patient supine and displacing the uterus rather than tilting the whole body. Left lateral tilt at the historical 15 to 30 degrees compromised compression quality and was largely retired as routine practice. If tilt is used at all, it is a fallback, and the priority is compression depth.

Is LUD done on every pregnant patient in cardiac arrest?

LUD applies once the uterus is large enough to compress the great vessels, which is about 20 weeks or a fundal height at the umbilicus. Earlier gestations generally do not need it. When gestational age is unknown, the bedside fundal height decides, and the safe default is to displace when the uterus reaches the umbilicus.

Who actually performs LUD during a code?

A designated rescuer, ideally assigned in advance as part of the maternal arrest plan, performs LUD continuously. In small teams that rescuer may also cover airway or IV tasks between compression cycles. In larger teams, the abdominal role should stay fixed across compressor rotations so displacement is never interrupted.

How hard should the rescuer push on the uterus?

Gentle but firm and steady, enough to move the uterus clearly left of midline without a shove. The goal is displacement, not pressure on the fetus or the abdominal wall. A two-handed pull from the patient's left is often easier to hold steadily than a fingertip push from the right.

Does LUD delay the decision about emergency delivery?

No. LUD and the delivery decision run in parallel. Displacement protects maternal circulation while the team assesses whether the uterus is at or above the umbilicus and whether the arrest has persisted long enough to warrant emergency delivery. LUD is a bridge, and delivery, when indicated, is the definitive relief of the compression.

Can the wedge or device replace hands entirely?

A wedge or commercial device can free both of a rescuer's hands for airway and IV work, which is its main advantage. The trade-offs are setup time and unfamiliarity on first use. Teams that stock a device should drill with it; teams without one should train the manual push as the default.

What happens if displacement is paused during compressor rotation?

The uterus drifts back toward the midline and compression efficiency drops until displacement resumes, which is why the role should transfer cleanly during hand-offs. Barnyard-quality hand-offs cost seconds that add up. A simple rule — the displacing hand stays on the abdomen until the next rescuer takes it — prevents most gaps.

This article is general educational information, not a diagnosis, treatment plan, or clinical protocol, and it makes no promise about outcomes. Follow the maternal cardiac arrest algorithm used by your own service or institution, and consult a qualified local clinician about any specific patient. For an active emergency, call your local emergency number immediately.